This invention relates to high solids thermosetting protective coatings and particularly to a blend of polyester and acrylic copolymer for use in high solids coatings further containing a hydroxyl functional urethane diluent. High solids coatings are non-aqueous coatings containing minor amounts of organic solvents and are particularly useful as coatings on appliances, aluminum extrusions, general metal surfaces, and wood substrates.
Acrylic polymers are known to generally provide useful coatings exhibiting good film properties. These polymers can contain reactive functional groups which are coreactive with other polymers or resins to provide thermosetting binder systems. Such acrylic binders can be produced by solution or bulk polymerization of ethylenically unsaturated monomers including acrylic monomers. Solvent can be added in minor amounts to render the acrylic polymer fluent. Various acrylic polymers have been suggested to provide high solids polymeric compositions such as disclosed in U.S. Pat. No. 4,374,164, or combined other polymers such as suggested in U.S. Pat. No. 4,397,989 or U.S. Pat. No. 4,369,283. Commonly assigned U.S. Pat. No. 4,716,200 issued Dec. 29, 1987 discloses low molecular weight acrylic copolymers combined with low molecular weight polyester polymer to provide high solids coatings whereas U.S. Pat. No. 4,397,989 discloses a high molecular weight acrylic copolymer in conjunction with a polyester polymer to provide acrylic high solids coatings.
Reactive diluents are described in U.S. Pat. No. 4,022,726 and U.S. Pat. No. 4,417,022, which described hydroxy functional urethane containing diluents. These diluents are characterized as having one primary or secondary hydroxyl group and have a retained solids value of greater than 80 percent by weight. The reaction of mono- and di-amines with monocyclocarbonates has been described by M. F. El-Giamal and R. C. Shultz, Makromol. Chem., 177(8), 2259 (1976), which discloses hydroxyl urethanes being furter reacted with isocyanates or acid functional materials to form alternating polyester-urethanes or copolyurethanes.
It now has been found that polyester acrylic polymeric blends useful in high solids coatings can be formulated with urethane containing diluents having hydroxyl functionality and provide good retention of the diluent in the coating film. These diluents have the added advantage that they have a large effect on the reduction of viscosity of a fluid coating and do not have an adverse effect on the final coating appearance or coating physical properties. These and other advantages of this invention will become more apparent by referring to the detailed description of the invention along with the illustrative examples.